I can't even claim to know anything about this as I'm childless, but my 6 year old niece is a handful for my brother and sis-in-law. She's been exceptionally stubborn (and nasty to her older sister by hitting, biting, pulling hair if she doesn't get her way) since she could walk. And some of the stuff that comes out of her mouth is utterly horrifying. And if looks could kill, we'd all be annihilated by now.

They enrolled her in karate about 6 months ago, and she LOVES it. She loves the structure, being graded, and advancing in belts.